Related art radio communications systems are based on the premise that there is a one-to-one correspondence between base stations and mobile communications terminals (e.g., mobile phones and mobile PCs), and therefore do not support services of transmitting data to two or more mobile communications terminals simultaneously using a base station. There is a previously known method of notifying broadcast information from a base station to all mobile communications terminals in the control area of the base station all at once using a common channel. However, this method is aimed at notifying information about control to all mobile communications terminals in the control area all at once, but is not aimed at transmitting data, such as audio data and image data, to all mobile communications terminals in the control area all at once.
In recent years, expectations have been running high for the use of multimedia services as mobile communications services. Particularly, the spotlight has been turned on a technology of simultaneously delivering multimedia data about sports live broadcasting, weather report, and radio, etc. to two or more mobile communications terminals.
There has been proposed a technology of, in addition to a first common channel (P-CCPCH: Primary-Common Control Physical Channel) which a base station uses when notifying broadcast information to two or more mobile communications terminals, providing a second common channel (S-CCPCH: Secondary-Common Control Physical Channel) which the base station uses when delivering signaling or multimedia data to two or more mobile communications terminals, and delivering multimedia data from the base station to two or more mobile communications terminals using the S-CCPCH (see patent reference 1 and nonpatent reference 1).
By thus delivering multimedia data using an S-CCPCH, a base station can simultaneously provide multimedia data to two or more mobile communications terminals. However, when a mobile communications terminal is located in the vicinity of the periphery of the control area of the base station, the electric wave transmitted from the base station may become weak and hence the reception quality of the electric wave may degrade even if the mobile communications terminal is staying in the control area of the base station.
To solve this problem, the base station has a function of controlling its transmission power so that the mobile communications terminal which has the smallest reception power in all the mobile communications terminals which are staying in the control area thereof will have reception power exceeding reference power.
On the other hand, each mobile communications terminal has a function of, when receiving the same multimedia data from two or more base stations, improving the reception quality by maximum-ratio-combining the two or more multimedia data.
However, since the propagation paths of two or more multimedia data from two or more base stations to each mobile communications terminal differ from one another, the receipt times when each mobile communications terminal receives the two or more multimedia data transmitted from the two or more base stations differ from one another, and therefore each mobile communications terminal cannot carry out maximum ratio combining of the two or more multimedia data if the receipt time difference becomes beyond a predetermined time period.
[Patent reference 1] JP,2003-188818,A
[Nonpatent reference 1] 3GPP Standardization Document R1-031103 Selective Combining for MBMS
A problem with related art radio communications systems constructed as mentioned above is that while a base station can secure the reception quality of each mobile communications terminal staying in the control area thereof by controlling its transmission power so that the mobile communications terminal which has the smallest reception power in all the mobile communications terminals which are staying in the control area thereof will have reception power exceeding reference power, an increasing of the transmission power assigned to the S-CCPCH may degrade the reception quality of information transmitted to a mobile communications terminal using another channel since the transmission power assigned to the other channel becomes low relatively.
Another problem is that while if each mobile communications terminal maximum-ratio-combines the same multimedia data transmitted from two or more base stations, each mobile communications terminal can improve the reception quality of the multimedia data without each base station controlling its transmission power, since the propagation paths of two or more multimedia data from the two or more base stations to each mobile communications terminal differ from one another, the receipt times when each mobile communications terminal receives the two or more multimedia data transmitted from the two or more base stations differ from one another, and therefore each mobile communications terminal cannot carry out maximum ratio combining of the two or more multimedia data if the receipt time difference becomes beyond a predetermined time period.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a mobile communications terminal and a radio communications system which can improve the reception quality of multimedia data without controlling the power required for transmission of the multimedia data by means of a base station.